Holddown force control for a scraper elevator



R. M. SMITH 3,466,764

HOLDDOWN FORCE CONTROL FOR A SCRAPER ELEVATOR Sept. 16,1969

2 Sheets-Sheet 1 Filed Dec. 9, 1966 INVENTOR. ROG-ER M. SNHTH R. M. SMITH Sept. 16, 1969 HOLDDOWN FORCE CONTROL FOR A SCRAPER ELEVATOR 2 Sheets-Sheet 2 Filed Dec. 9, 1966 OKIVENTORLI ROG-ER M SNHTH RESERVOIR I- llll II llll p7,. ATTORNEYS United States Patent 3,466,764 HOLDDOWN FORCE CONTROL FOR A SCRAPER ELEVATOR Roger M. Smith, J oliet, Ill., assignor to Caterpillar Tractor Co., Peoria, 11]., a corporation of California Filed Dec. 9, 1966, Ser. No. 600,514 Int. Cl. E02f 3/ 76 US. Cl. 37-8 5 Claims ABSTRACT OF THE DISCLOSURE A fluid motor powered elevator of a self-loading scraper is pivoted to the bowl thereof whereby it may swing upward and forward from the cutting edge to adjust to varying depths of cut. Elevator holddown force, supplementary to gravity, is provided by a fluid operated cylinder and piston assembly connected between the elevator and the bowl and communicated with the driving fluid input to the elevator motor. The holddown force is thereby varied in accordance with the forces tending to lift the elevator inasmuch as an increase in elevator loading causes a pressure rise at the elevator motor fluid intake which in turn increases the downward force exerted on the elevator by the holddown cylinder.

This invention relates to powered earthmoving equipment and more particularly to mechanism for varying the holddown force on the elevator of a self loading scraper to optimize elevator action.

In the operation of tractor drawn scrapers of the class having a load carrying bowl with a cutting edge at the forward face, the contents of the partially filled bowl tend to resist the entrance of additional material. Consequently it has become a common practice to equip such scrapers with an elevator at the forward portion of the bowl to assist the movement of earth across the cutting edge and up into the bowl. Such scrapers are self loading under most conditions and thus do not require supplementary motive power, in the form of a pusher tractor or the like, which may otherwise be needed to insure complete loading.

The volume of earth or other material which passes over the cutting edge and into the bowl will vary during operation and relatively thick solid objects such as rocks or the like may present. To accommodate to these variables, the elevator must be capable of a limited amount of movement with respect to the cutting edge. This is generally provided for through the mounting structure which attaches the elevator to the scarper bowl. In most such structures the elevator is carried on pivots which allow the lower end of the elevator to swing upward and forward from the cutting edge when it is necessary that the opening therebetween increase.

The elevator flights react against the material being loaded in such a manner as to create a turning moment which tends to pivot the elevator upward from the cutting edge to a greater extent than is desirable. Accordingly provision must be made for exerting a counter-balancing holddown force on the elevator. In some prior constructions this has been provided solely by the weight of the elevator itself and in other instances springs have been employed to produce supplementary holddown force. In either case, the magnitude of the holddown force has been almost constant or has varied solely as a function of the angular position of the elevator. Thus prior techniques do not relate the holddown force, in any optimum way, to the turning moment exerted against the elevator by the material being loaded.

The prior constructions have not realized the most efficient elevator action inasmuch as, in operation, the op- "Ice timum amount of holddown force varies substantially under different conditions. More specifically, the turning moment which tends to lift the elevator varies in accordance with the reaction against the elevator flights by the material being loaded and the holddown force should be varied accordingly.

If, for example, a very strong cohesive material or an unusually heavy material is being loaded a larger than normal loading of the elevator occurs. This causes the elevator to tend to withdraw from the cutting edge to an excessive extent and in an extreme case the elevator may more or less override the material which is being loaded. To avoid this effect, holddown force should be increased as the loading of the elevator increases. Under the opposite conditions, where the loading of the elevator decreases, the holddown force should be reduced as the elevator tends to move too close to the cutting edge and the height of the passage into the bowl is excessively restricted.

The present invention avoids these inefficiencies by varying the holddown force in accordance with variations in the forces tending to lift the elevator.

The torque exerted on the elevator drive by the elevator motor is proportional to the lifting forces inasmuch as it is changes in the loading of the elevator which produce the changes in the lifting force. Accordingly, in the common case where the elevator is operated by a hydraulic motor, the variable controlled holddown force can conveniently be derived from a hydraulic cylinder having a port communicated with the driving fluid input to the motor. As pressure at the motor input increases when the torque output of the motor increases, the holddown force is automatically varied in the optimum manner.

Accordingly it is an object of this invention to provide for more efiicient elevator action in a self loading scraper.

It is another object of this invention to vary the holddown force on the elevator of a self loading scraper in accordance with the counterforces thereon.

It is another object of this invention to provide means for varying the holddown force on the elevator of a self loading scraper in an optimum manner while providing for maximum freedom of movement of the elevator.

It is still another object of this invention to improve the operation of self loading scrapers where materials having differing characteristics are to be loaded.

The invention, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in conjunction with the accompanying drawing of which:

FIGURE 1 is .a side elevation view of a self loading scraper with portions of the bowl sidewall and associated elements broken out to better illustrate the elevator and mounting structure therefor;

FIGURE 2 is a side elevation view of the elevator region of the scraper of FIGURE 1 showing one form of positional change which the elevator may undergo in response to variable loading conditions and showing certain of the hydraulic circuit elements in schematic form;

FIGURE 3 is a partial section view taken along line IIIIII of FIGURE 2 showing further details of mounting structure at the top of the elevator; and

FIGURE 4 is a view taken along line IV-lV of FIGURE 2 and illustrating motion limiting structure at the lower end of the elevator.

Referring now to the drawing and more particularly to FIGURE 1 thereof, 'a scraper 11 of the type to which the invention is applicable will typically have a load carrying bowl 12 with sidewalls 13 and a cutting edge 14 carried at the lower edge of the open forward face thereof. To support the bowl 12 at the back end, frame members 1.6 extend rearwardly and connect with rear wheels 1.7.

The scraper is drawn by a tractor 18 which is coupled to the bowl 12 through a gooseneck 19 and a pair of draft arms 21 which extend along opposite bowl sidewalls 13 and connect to centrally located points thereon through pivots 22. To control the elevation of the cutting edge 14 relative to the ground surface 23, a pair of hydraulic jacks 24 are connected between the forward portion of the bowl 12 and the spreader arm 26 which couples draft arms 21 to the gooseneck 19. Thus extension of the jacks 24 pivots the entire bowl 12 including the cutting edge 14, downwardly about the axis of rear wheels 17 so that the edge may be caused to bite into the ground surface 23 and guide a superficial layer of soil upwardly into the bowl. Contraction of the jacks 24 pivots the bowl 12 and cutting edge 14 upwardly away from the ground surface to the load carrying position.

To discharge the load from bowl 12, ejection mechanism is provided which in this example is comprised of a rectractable floor section 27. Floor section 27, in the closed position, extends from the cutting edge support 28 to the arcuate rear wall 29 of bowl 12 and is supported by triangular side members 31 extend upward and attach to the bowl sidewalls 13 at pivots 32, A pair of hydraulic jacks 33 are connected between the rear frame members 16 and linkage 34 which connects to the underside of the floor section 27 so that contraction of the jacks swings the floor section rearwardly and upward to release material from the bottom of bowl 12.

In self loading scrapers of this general type, the movement of earth across the cutting edge 14 and up over support 28 into bowl 12 is assisted by a chain and flight elevator 36 disposed at the forward portion of the bowl. The elevator 36, which also functions to retain material at the open front face of the bowl 12, is mounted with the lower end above and slightly forward from the cutting edge 14 and extends upward and rearwardly therefrom. Salient elements of the elevator 36 include a rectangular frame with side members 37 and endless chains 38 carrying transverse flights 39 and carried on drive sprockets 41 at the top of the elevator and idlers 42 at the base thereof. Rollers 43 are spaced along the forward faces of the frame side members 37 to aid in supporting the chains 38.

The elevator 36 cannot be rigidly fixed relative to the bowl 12 inasmuch as the lower end of the elevator must be free to move upward from the cutting edge 14 to adjust to varying depths of cut and to override obstacles such as rocks and the like which might otherwise jam or damage the elevator. Referring now to FIGURE 2, this motion is provided for by coupling the upper end of the elevator 36 to the bowl 12 by means of a pivot connection 44 to arms 46 which project upward from the bowl sidewalls 13. Thus the lower end of the elevator 36 may swing upward and forward from cutting edge 14 when necessary to a position such as that illustrated by dashed lines 36'.

Most prior self loading scrapers have employed an elevator mounting which limits the movement of the lower end of the elevator to a fixed arcuate path in the manner described above. This curvilinear forward and upward motion of the lower end of the elevator provides for a maximum change in the distance between the elevator and the cutting edge 14 with a minimum of elevator motion. However in many instances the forces which act on the elevator may be more or less in direct alignment with the plane of the elevator frame and the inability of the elevator to move along that plane increases the likelihood of damage. Accordingly in the present invention the coupling between the upper end of the elevator 36 and bowl sidewall arms 46 is arranged to provide for longitudinal upward movement of the elevator in addition to the pivoting motion described above.

Referring now to FIGURE 3 in conjunction with FIG- URE 2, the elevator 36 is capable of linear movement in its own plane inasmuch as the pivot pins 47 which couple the elevator to the bowl sidewall arms 46 extend into blocks 48 which are slidable within longitudinal tracks 49 formed in the elevator frame sidemembers 37. A compression spring 51 is disposed within each track 49 to urge the elevator frame member 37 downwardly relative to block 48. Thus if a force is imposed on the lower end of the elevator 36 in a direction parallel to the plane of the elevator frame, the entire elevator assembly may move upwardly against the action of springs 51. Should the elevator experience a combination of forces which tend both to move it linearly in its own plane and also to pivot it upwardly and forwardly, it is free to undergo any combination of such motions.

Downward motion of the elevator 36 in its own plane is limited by abutment of the top of tracks 49 against the blocks 48. Referring now to FIGURE 4 in combination with FIGURE 2, pivoting of the elevator 36 towards the cutting edge 14 is limited by abutment of a lateral projection 52 at the lower end of each elevator frame sidemember 37 against a stop 53 which projects a small distance inwardly from each bowl sidewall 13. Thus the flights 39 of the elevator 36 are kept from contact with the cutting edge 14.

While the elevator 36 should be free to move away from the cutting edge 14 as described above, it is also necessary that means be provided to yieldably resist such motion so that the lower end of the elevator is held in engagement with the material to be loaded. Some of this holddown force is inherent in the structure inasmuch as the pivot connection 44 at the upper end of the elevator is above and behind the lower end thereof so that the weight of the elevator tends to produce the desired result. In many prior constructions this effect is relied upon to provide all of the holddown force while some other prior scrapers also use springs connected between the elevator and the bowl to supplement the gravity force. In either instance the magnitude of the holddown force is a function solely of the angular position of the elevator relative to its upper pivot and is not meaningfully related to the instantaneous loading of the elevator.

As a practical matter the optimum holddown force for most efficient elevator operation varies considerably at different times. Such factors as changes in the characteristics of the material being loaded and changes in the amount of material in the bowl have a pronounced effect on the loading of the elevator and if the holddown force does not vary accordingly the flights 39 may bite too deeply into the material being loaded and restrict the passage into the bowl or may lift and tend to override the material. To overcome this effect, the present invention provides for varying the holddown force in response to changes in elevator loading.

This is most efficiently done by making use of the fact that the driving fluid pressure at the input to the hydraulic motor 54 which operates the elevator varies in proportion to the loading thereon. The hydraulic motor 54 is generally situated at the top of the elevator and is operated by a high pressure fluid such as oil supplied from a pump 56 through an intake conduit 57. Pump 56 draws oil from a reservoir 58 and a return conduit 59 extends from the motor outlet to the reservoir.

Operation of the elevator 36 is controlled by a spool valve 61 disposed between the pump 56 and motor intake conduit 57. Valve 61 has a first position at which high pressure fluid from pump 56 is delivered to motor 54 through conduit 57 and has a second position at which the fluid flow from the pump is returned directly to the reservoir 58 thereby bypassing the motor and stopping the elevator. To protect the hydraulic circuit against overpressures, a relief valve 62 is connected between the outlet of pump 56 and the conduit 63 which returns the fluid from valve 61 directly to the reservoir at the second position of the valve.

To generate a holddown force on the elevator 36 which is proportional to the fluid pressure between motor 54 and pump 56, one of a pair of hydraulic cylinder assemblies 64 is connected between each bowl sidewall 13 and the lower portion of the corresponding elevator frame sidemember 37. In a preferred form, each such assembly 64 has a cylinder member 66 with one end coupled to the bowl sidewall 13 by a pivot 67 A slidable piston 68 within cylinder 66 has a rod 69 coupled thereto which extends along the axis of the cylinder and projects therefrom to connect to the elevator frame sidemember 37 at a pivot coupling 71. A conduit 72 connects the motor intake conduit 57 with the end of cylinder 66 which is remote from pivot 67 and a vent and leakage oil return line 75 extends from the opposite end of the cylinder to reservoir 58.

In operation, the pressure of the motor driving fluid reacts against the piston 68 in each cylinder 66 to produce a holddown force which is transmitted to the elevator 36 through rods 69 and pivots 71. Further, such holddown force varies automatically with variations in the loading of the elevators 36. Thus an increase in the forces resisting motion of the elevator flights 39 produces a compensating pressure rise in the motor intake conduit 57. The increased pressure is transmitted to cylinder 66 by conduit 72 and reacts against the piston 68 to increase the holddown force. A reversed effect occurs if the elevator flights 39 encounter a decreased resistance inasmuch as the resulting pressure drop within the motor intake conduit 57 is similarly transmitted to the cylinder 66. Thus the cylinder assemblies 64 vary the holddown force automatically and in an optimum manner.

The holddown force generating cylinder assembly 64 may be made fully compatible with the maximized freedom of movement of the elevator 36 as hereinbefore described. The elevator 36 may pivot forwardly and upward from cutting edge 14 about the upper pivot connection 44 as hereinbefore described inasmuch as the piston 68 can travel forwardly within cylinders 66 against the fluid pressure therein. Movement of the elevator 36 upwardly and backwardly within its own plane as hereinbefore described would be prevented if the piston 68 within cylinder 66 were allowed to bottom out against the end of the cylinder at the start of such movement. To avoid this effect, the cylinder 66 is proportioned to provide ample clearance space 73 to allow movement of the piston 68 in the direction of pivot 67 as needed to effect the longitudinal movement of the elevator. If desired, a compression spring 74 may be disposed in the cylinder 66 to urge piston 68 in the direction of pivot 67. Such a spring 74 will tend to reduce unwanted pivoting of the elevator 36 from miscellaneous pressure fluctuations which may occur in the hydraulic circuit.

While a specific embodiment of the invention has been described herein, it will be apparent that many variations and modifications are possible within the scope of the invention and it is not intended to limit the invention except as defined in the following claims.

Iclaim:

1. In a scraper of the class having a bowl with a cutting edge and a movable elevator above said cutting edge, said elevator being driven by a fluid motor having a driving fluid intake, mechanism for providing a holddown force on said elevator comprising fluid operated force generating element coupled between said elevator and said bowl to urge said elevator toward said cutting edge, said force generating element having a fluid input communicated with said driving fluid intake of said elevator motor whereby said holddown force varies in accordance with changes in loading of said elevator.

2. In a scraper of the class having a bowl with a cutting edge and a movable elevator above said cutting edge wherein said elevator is operated by a fluid powered motor mechanism for providing a holddown force on said elevator comprising a controllable force generating element coupled between said elevator and said bowl to urge said elevator toward said cutting edge wherein said controllable force generating element comprises a cylinder having an end communicating with the driving fluid intake of said motor, a slidable piston therein, and a rod extending into said cylinder and coupled with said piston therein, said element being pivotably coupled to said elevator and pivotably coupled to said bowl, said communication of said cylinder end with said fluid intake of said motor being a control means which varies the holddown force produced by said element in accordance with changes in the loading of said elevator.

3. The combination defined in claim 2 and further comprising a resilient element coupled between said elevator and said bowl to resist movement of said elevator away from said cutting edge.

4. The combination defined in claim 2 and further comprising a spring disposed within said cylinder and acting against said piston therein to resist movement of said elevator away from said cutting edge.

5. The combination defined in claim 2 wherein said elevator is pivoted to said bowl at the top of said elevator and stops are secured to said bowl to limit downward pivoting movement of said elevator toward said cutting edge and wherein said elevator is movable longitudinally within a plane containing the pivot axis of said elevator, said controllable force generating element having a first end pivoted to said elevator and having the opposite end pivoted to said bowl rearwardly from said elevator and being contractible to a greater extent than required to contact said elevator with said stops when said elevator is at its lowermost position with respect to said longitudinal movement thereof whereby said elevator may lift longitudinally without also being forced away from said stops.

References Cited UNITED STATES PATENTS 2,546,907 3/1951 Sherwood 37-8 2,984,022 5/1961 Johnson 378 3,143,814 8/1964 Brinkmeyer et al 378 3,210,868 10/1965 Liess 378 3,334,428 8/1967 Rezabek 378 3,343,286 9/1967 Ray et al 378 ROBERT E. PULFREY, Primary Examiner E. H. EICKHOLT, Assistant Examiner US. Cl. X.R. 37129 

